Agilent Technologies E3630A service manual Maintenance, Test Equipment Required

put is enclosed by a heavy line in Figure 3 of the operating section. If the operating point reaches the diagonal current limit line, a decrease in load resistance moves the operating point down the line, reducing the output voltage and current. Current foldback is controlled by a second operational ampli- fier (current comparison amplifier) in the regulator that moni- tors the dc output current. This current comparison amplifier takes control of the output away from the voltage comparison amplifier when the current reaches the design limit. Removing the overload restores constant voltage operation auto- matically.

The 0 to +20-volt regulator has a fixed current limit at 105% of its 0.5 amp maximum rated output. The input ac line voltage is first applied to the preregulator which operates in conjunc- tion with the SCR control circuit (preregulator control circuit) to rectify the tap switched AC voltage. This preregulator mini- mizes the power dissipated in the series regulating elements by controlling the dc level across the input filter capacitor, depending on the output voltage. To achieve this, tap switch- ing is accomplished by two SCRs and one bridge diode (CR28, CR32 and CR26) and the SCR control circuit. This cir- cuit allows the input capacitor to charge to one of two discrete voltage levels depending on the output required.

When output voltage exceeds the reference level, the SCR control circuit fires two SCRs that cause the input capacitor to be charged to the voltage which is necessary for full output of the supply. When the two SCRs are not fired, the bridge diode CR26 conducts and half the voltage is applied to series pass transistor Q9.

The 0 to -20-volt regulator is, in turn, similar to the +20-volt regulator except that it resembles a complementary mirror image of the latter. The output voltages of the +20-volt and - 20-volt supplies are both set by the same front panel control and track each other within 1% in the fixed tracking ratio mode. Precise tracking of the two outputs is achieved by controlling the positive output conventionally and using that output as the reference voltage for the negative output.

The reference and bias supply powers the operation amplifi- ers and provides reference and bias voltages for the output regulators. The display power circuit provides voltage which is used by the A/D converter and display.

The turn-on/turn-off control circuit prevents output transients when the supply is turned on or off. It does this by delaying the application of certain bias and reference voltages at turn- on and removing them shortly after turn-off.

Three meter push-button switches select which of the sup- plies has its output voltage and current indicated on the front panel meters.

Diode CR2, CR3, and CR4 are connected across the output terminals in reverse polarity. They protect the output elec- trolytic capacitor and the series regulator transistors from a reverse voltage applied across the output terminals.

MAINTENANCE

INTRODUCTION

This section provides performance test, troubleshooting infor- mation, and adjustment and calibration procedures. The fol- lowing operation verification tests comprise a short procedure to verify that the power supply is performing properly, without testing all specified parameters.

If a fault is detected in the power supply while making the performance check or during normal operation, proceed to the troubleshooting procedures. After troubleshooting, per- form any necessary adjustments and calibrations. Before returning the power supply to normal operation, repeat the performance check to ensure that the fault has been properly corrected and that no other faults exist.

Test Equipment Required

The following Table A-1 lists the equipment required to per- form the various procedures described in this section.

Table A-1. Test Equipment Required

TYPE	REQUIRED CHARACTERISTICS	USE	RECOMMENDED
			MODEL
Oscilloscope	Sensitivity : 100 mV	Display transient response and ripple	Agilent 54600A
	Bandwidth : 20 MHz/100 MHz	and noise waveforms.
RMS Voltmeter	True rms, 20 MHz bandwidth	Measure rms ripple and noise
	Sensitivity : 1 mV	voltage.
	Accuracy : 5%
Multimeter	Resolution : 100 nV	Measure dc voltages.	Agilent 34401A
	Accuracy : 0.0035%
Electronic Load	Voltage Range : 240 Vdc	Measure load and line regulation.	Agilent 6063A
	Current Range : 10 Adc
	Open and short switches
	Transient on/off
Resistive Loads (RL)	40 W 20 W, 2.4 W 20 W	Measure ripple and noise.

A-2